Yes, I know it's comical the amount of threads started because of the infamous IIsi power supply. Naturally, I'm joining in the fun and creating another! Hopefully this will spark more discussion around what could be the culprit with them. Okay - here's the issue with mine: it powers on, then turns right off (most of the time).
I have done a complete recap of both the main board and daughtercard. I cleaned everything I could with a toothbrush and IPA after the recap. I then tossed it in the ultrasonic for two minutes to get the nooks 'n crannies.
During initial testing, I'd hit power on the logic board, and the PSU solenoid would click on then immediately off. After leaving it sit for a while, I tried again and it stayed on. Power cycling a few times caused the PSU to turn itself off once or twice, but was generally stable.
Given the attention that the daughtercard draws as a potential failure point, I swapped sub boards with a known working power supply. No dice. The previously working unit continued to work and my broken unit continued to power on then off right away.
Then, I turned my attention to the thermal resistor which closes during overheating, thinking that was falsely too hot to run. Completely disconnected this component - no change. Bridging it together causes shutdown (as is expected).
I then de soldered the large inductor at the corner of the board - all clean and no gunk. Ultrasonic did its job! Also removed a couple of diodes around the large 250V caps - all working well.
As a last-ditch effort, I touched up any solder joints on the rear looking slightly suspect. No change.
In summary, the intermittent issue of powering itself off is not due to the following:
I have done a complete recap of both the main board and daughtercard. I cleaned everything I could with a toothbrush and IPA after the recap. I then tossed it in the ultrasonic for two minutes to get the nooks 'n crannies.
During initial testing, I'd hit power on the logic board, and the PSU solenoid would click on then immediately off. After leaving it sit for a while, I tried again and it stayed on. Power cycling a few times caused the PSU to turn itself off once or twice, but was generally stable.
Given the attention that the daughtercard draws as a potential failure point, I swapped sub boards with a known working power supply. No dice. The previously working unit continued to work and my broken unit continued to power on then off right away.
Then, I turned my attention to the thermal resistor which closes during overheating, thinking that was falsely too hot to run. Completely disconnected this component - no change. Bridging it together causes shutdown (as is expected).
I then de soldered the large inductor at the corner of the board - all clean and no gunk. Ultrasonic did its job! Also removed a couple of diodes around the large 250V caps - all working well.
As a last-ditch effort, I touched up any solder joints on the rear looking slightly suspect. No change.
In summary, the intermittent issue of powering itself off is not due to the following:
- soft power daughtercard
- leaked electrolytic fluid under inductors
- TH101 resistor
- thermal switch
- solder joints
